Cigarette smoking has well documented health risks, an economic burden of over $167 billion annually, and provides only modest hedonic effects, yet one in five adults continues to smoke. The aim of the proposed project will be to uncover a potential mechanism for the maintenance of nicotine dependence-increasing reward to social stimuli, which would reinforce social situations in which people tend to smoke. An effect of nicotine on social information processing, as evidenced by differences in attention bias and evaluation of emotion intensity, would suggest that smokers experience greater reward from positive social stimuli or perceive less threat from negative social stimuli after ingesting nicotine. Considering the pervasiveness of social situations in which smoking occurs, such an effect might explain why smokers accept the risk of health consequences. The goal of this project is twofold: (1) examine how chronic smokers process emotion valence and intensity in facial expressions, and (2) determine whether nicotine ingestion has a direct effect on how smokers process facial expressions. We will enroll 132 smokers, 66 chronic, nicotine-dependent smokers and 66 occasional, non-dependent smokers. To address the first goal, all smokers will abstain from nicotine for 24 hours prior to completing tasks to measure reaction times and accuracy in detecting emotions in human faces. We hypothesize that chronic smokers will have an attention bias toward negative (angry, disgust) emotion expressions and will overestimate the intensity of these negative expressions, while occasional smokers will have a bias toward positive (happy) emotion expression. Because the differences expected in chronic smokers may be due to nicotine withdrawal, we plan to disentangle the chemical effects of nicotine from withdrawal symptom relief. The second part of the project will involve participants smoking either a nicotine-containing or placebo cigarette prior to completing behavioral tasks. We will analyze the direct effects of nicotine on how people perceive facial expressions by comparing reaction times and accuracy with data from the first trial before the cigarette. Previous research suggests that nicotine increases susceptibility to reward stimuli. Acute nicotine administration is therefore expected to increase attention and intensity bias for happy faces compared to placebo. When comparing with occasional smokers, we expect chronic smokers to experience greater changes in social information processing; this would suggest that nicotine ingestion may attenuate the adverse social-emotional consequences of nicotine withdrawal. Secondary aims of this research will address possible moderators of these effects: emotion regulation strategies, social anxiety, gender, and motivations for smoking. Since more than 95 percent of individuals who attempt to quit smoking fail, this study would be an important contribution to inform treatment of nicotine dependence. A social enhancement effect of cigarette smoking would suggest cognitive-behavioral techniques to be of particular value in helping smokers quit.